1. Technical Field
The present invention pertains to improvements in methods and apparatus for heating or cooling sterile surgical liquids and collecting surgical sterile slush. In particular, the present invention is an improvement of the methods and apparatus disclosed in U.S. Pat. No. 4,393,659 (Keyes et al), U.S. Pat. No. 4,934,152 (Templeton), U.S. Pat. No. 5,163,299 (Faries, Jr. et al), U.S. Pat. No. 5,331,820 (Faries, Jr. et al), U.S. Pat. No. 5,333,326 (Faries, Jr. et al), U.S. Pat. No. 5,457,962 (Faries, Jr. et al), U.S. Pat. No. 5,522,095 (Faries, Jr. et al), U.S. Pat. No. 5,524,643 (Faries, Jr. et al) and U.S. Pat. No. 5,615,423 (Faries, Jr. et al), and copending U.S. patent application Ser. No. 08/807,095, entitled "Surgical Drape and Stand for Use in Thermal Treatment Basins", filed Feb. 27, 1997. The disclosures of the aforementioned patents and copending patent application (i.e., U.S. patent application Ser. No. 08/807,095) are incorporated herein by reference in their entireties.
2. Discussion of Related Art
The above-referenced Keyes et al patent (U.S. Pat. No. 4,393,659) discloses a surgical slush producing system having a cabinet with a heat transfer basin located at its top surface. A refrigeration mechanism in the cabinet takes the form of a closed refrigeration loop including: an evaporator in heat exchange relation to the outside surface of the heat transfer basin; a compressor; a condenser; and a refrigeration expansion control, all located within the cabinet. A separate product basin is configured to be removably received in the heat transfer basin. Spacers, in the form of short cylindrical stubs or buttons, are arranged in three groups spaced about the heat transfer basin and projecting into the heat transfer basin interior to maintain a prescribed space between the two basins. During use, that space contains a thermal transfer liquid, such as alcohol or glycol, serving as a thermal transfer medium between the two basins. A sterile drape, impervious to the thermal transfer medium, is disposed between the product basin exterior and the liquid thermal transfer medium to preserve the sterile nature of the product basin. Surgically sterile liquid, such as sodium chloride solution, is placed in the product basin and congeals on the side of that basin when the refrigeration unit is activated. A scraping tool is utilized to remove congealed sterile material from the product basin side to thereby form a slush of desired consistency within the product basin. Some users of the system employ the scraping tool to chip the solid pieces from the basin side.
As noted in the above-referenced Templeton patent (U.S. Pat. No. 4,934,152), the Keyes et al system has a number of disadvantages. In particular, the separate product basin must be removed and re-sterilized after each use. Additionally, the glycol or other thermal transfer medium is typically highly flammable ortoxic and, in any event, complicates the procedure. The Templeton patent discloses a solution to these problems by constructing an entirely new apparatus whereby the product basin is eliminated in favor of a sterile drape impervious to the sterile surgical liquid, the drape being made to conform to the basin and directly receive the sterile liquid. Congealed liquid is scraped or chipped from the sides of the conformed drape receptacle to form the desired surgical slush.
The Faries, Jr. et al patent (U.S. Pat. No. 5,163,299) notes that scraping congealed liquid from the drape is undesirable in view of the potential for damage to the drape, resulting in a compromise of sterile conditions. As a solution to the problem, the Faries, Jr. et al patent (U.S. Pat. No. 5,163,299) proposes that the drape be lifted or otherwise manipulated by hand to break up the congealed liquid adhering to the drape. Although this hand manipulation is somewhat effective, it is not optimal, and often is inconvenient and constitutes an additional chore for operating room personnel.
The Faries, Jr. et al patent (U.S. Pat. No. 5,331,820) resolves the problem of manual manipulation of the drape by providing a method and apparatus to automatically remove congealed liquid adhering to the drape without endangering the integrity of the drape. A flat disk or plate is typically provided at the bottom of the basin under the drape. The plate is moved in an up and down manner to manipulate the drape and disengage the congealed liquid adhering to the drape. The plate may be attached to a mechanism below the basin, or to the drape itself as disclosed in the Faries, Jr. et al patent (U.S. Pat. No. 5,457,962).
In addition to accommodating surgical slush, the Templeton patent provides an electrical heater disposed at the bottom of the basin to convert sterile surgical slush to warmed sterile liquid, or to heat additional sterile liquid added to the basin. The electrical heater typically includes a heating element in the form of a thin wafer having a circular opening defined at the center of the heating element. A threaded stud projects through the opening to engage a heating plate via a nut and lock washer. The heating plate serves to dissipate excess heat from the heating element within a system cabinet and to aid in securing the heating element against the basin. The lock washer is typically constructed of an insulating material to minimize heat transfer between the heating element and stud, thereby preventing formation of a hot spot at the center of the basin floor that may melt the drape during system operation. The Templeton patent describes the need for warm sterile liquid as occurring after a surgical procedure is completed to facilitate raising the body cavity of the surgery patient back to its normal temperature by contact with the warmed liquid. However, there are a number of instances during a surgical procedure when it is desirable to have simultaneous access to both warmed sterile liquid and sterile surgical slush. For example, if the surgical slush is not of a desired consistency (e.g., too thick), the availability of warm sterile liquid to be added to the slush permits rapid adjustability of slush consistency. Likewise, maintaining instruments at or near body temperature during surgery is a desirable feature permitted by warm sterile liquid. Generally, if warm sterile liquid is simultaneously available with surgical slush, there is no need to wait for the slush to melt at the end of the surgical procedure. Moreover, the simultaneous provision of sterile surgical slush and warm sterile liquid permits the two to be comprised of different compounds as is sometimes necessary for various surgical procedures.
In response to the foregoing need for simultaneous availability of warmed sterile liquid and sterile surgical slush, the Faries, Jr. et al patents (U.S. Pat. Nos. 5,333,326, 5,522,095 and 5,524,643) disclose a thermal treatment system of the type having at least a warming basin for containing warm surgical liquid and a surgical slush or cooling basin of the type disclosed in the Templeton patent. The warming basin may be implemented as a separate unit and secured to a pre-existing surgical slush system (e.g., a thermal treatment system having a cooling basin to produce surgical slush), may be constructed as part of an integral cabinet that houses warming and cooling basins, or may be implemented as a separate unit and attached to an individual surgical slush unit a (e.g., a cooling basin producing surgical slush that is implemented as an individual unit) with the warming and surgical slush units supported by a common base. A large surgical drape covers both the warming and cooling basins and contains the warm surgical liquid and surgical slush in a sterile manner. In addition, the drape may include centering indicia to direct placement of the drape over the thermal treatment system and within each basin.
Typically, a sterile surgical drape is placed over a single or multiple basin thermal treatment system with a portion of the drape disposed within each thermal treatment system basin to form a drape receptacle within each basin for containing a sterile liquid or medium. The sterile liquid contained and warmed within a thermal treatment system warming basin may be utilized to heat objects (e.g., medical instruments, containers, pitchers, etc.) placed within that basin. However, placement of objects within the warming basin may puncture the drape in several different ways, thereby compromising sterility of the warm sterile liquid and possibly an entire surgical procedure. For example, objects placed within the warming basin may trap air between the object base and drape material. The trapped airtypically expands beneath the object when heated and expels sterile liquid from beneath the object, thereby permitting the drape to absorb additional thermal energy from the warming basin at locations where liquid has been expelled. The additional thermal energy causes the drape to overheat, melt and stick to the warming basin, thereby forming holes. Further, the drape material may soften significantly when exposed to the heated basin floor, thereby allowing normally safe (e.g., dull or blunt) objects to puncture the material (e.g., blunt plastic syringe tips and blunt tipped hemostats). Moreover, lack of sufficient liquid in the warming basin due to user error or evaporation tends to increase the amount of thermal energy absorbed by the drape, thereby causing portions of the drape to overheat forming hot spots and pinholes. Since a warming basin heater covers substantially the entire basin floor, the basin is continuously supplied or saturated with thermal energy from that heater and cannot further conduct thermal energy to reduce the amount of thermal energy absorbed by the drape, thereby enabling drape damage as described above.
Heating stainless steel objects within the warming basin, such as pitchers or graduates, tends to reduce drape damage since the stainless steel objects conduct heat from the contact site (e.g., contact site between the object and drape or basin), thereby reducing the amount of thermal energy absorbed by the drape. However, stainless steel objects tend to be expensive, while a substantial amount of medical objects are constructed of plastic. The plastic objects absorb a minimal amount of thermal energy, thereby enabling the drape to absorb thermal energy from the warming basin in amounts sufficient to cause damage to the drape as described above. The Templeton patent attempts to overcome the problem of drape melting within a warming basin during system operation by preventing formation of a hot spot at the center of the basin floor. This is accomplished by minimizing heat transfer between a heating element located at the bottom of the basin and a stud, disposed adjacent the basin bottom, that extends through a heating element central opening as described above. However, the stud and/or heating element central opening each are of a relatively small size in comparison with the basin floor and cannot conduct sufficient amounts of thermal energy to substantially reduce the amount of thermal energy absorbed by the drape when objects are placed in the basin. Thus, the drape is permitted to absorb excess thermal energy from the warming basin that may damage the drape in substantially the same manner described above when objects are placed in the basin.
Copending U.S. patent application Ser. No. 08/807,095 discloses a system to overcome the aforementioned problems of heating objects within warming basins by including a stand to elevate the objects above the heated basin floor and prevent damage to a drape. The stand may be implemented as a separate unit for placement within a warming basin or be disposed on and integral with the drape. However, the technique disclosed in the copending application may stand some improvement. In particular, it is desirable to prevent damage to the drape when heating objects within the warming basin without introducing additional components into the system that may require sterilization or replacement prior to each use, thereby creating additional chores for operating room personnel. For example, operating room personnel may be required to sterilize the stand and/or verify the presence of the stand within the warming basin prior to heating objects within that basin to ensure sterile conditions. Further, additional system components tend to increase system complexity and cost, while providing another manner in which the sterile liquid or medium contained within the warming basin may become contaminated during a surgical procedure.
Generally, a sterile surgical drape is disposed over a thermal treatment system as described above to essentially form a sterile field above each basin to maintain sterility of a sterile liquid or medium. Since the sterile surgical drape provides a sterile field above each basin for the sterile liquid, it is important that the drape be properly positioned on the thermal treatment system to prevent contamination of the sterile liquid and a surgical procedure. Accordingly, the Faries, Jr. et al patent (U.S. Pat. No. 5,615,423) discloses a surgical drape having various indicia to assist an operator in properly placing the surgical drape over the thermal treatment system and within warming and/or cooling basins to ensure sterility of the sterile liquid. The indicia may be disposed on drapes for use with single or multiple basin thermal treatment systems. In addition, the aforementioned Faries, Jr. et al patents (U.S. Pat. Nos. 5,333,326, 5,522,095 and 5,524,643) disclose a surgical drape for a multiple basin thermal treatment system having centering indicia to direct placement of the drape on the thermal treatment system and within each thermal treatment basin as described above.
The apparatus and/or drapes disclosed in the above-mentioned patents may stand some improvements to ensure sterile conditions. In particular, the Faries, Jr. et al patents (U.S. Pat. Nos. 5,333,326, 5,522,095, 5,524,643 and 5,615,423) disclose drapes having indicia to facilitate proper deployment of the drapes on a thermal treatment system as described above, however, operating room personnel or other users determine whether or not a drape is properly positioned on the thermal treatment system, thereby providing a margin for human error that may produce non-sterile conditions from an improperly positioned drape. Further, the drape generally requires continuous monitoring during system operation to ensure that the drape maintains its position on the thermal treatment system to provide the sterile field. If the drape is improperly positioned or shifts during system operation, the sterile field may become contaminated, thereby compromising the sterility of the entire surgical procedure. Although operating room personnel can be advised and cautioned about the importance of properly placing a drape over a thermal treatment system prior to the performance of a surgical procedure, there is no assurance that carelessness will not result in operation of a thermal treatment system without the proper placement and/or use of the drape on the system. Thus, it is desirable to automatically detect the proper positioning and/or presence of a drape on a thermal treatment system to ensure the drape provides a sterile field and maintains sterility of sterile liquid during a surgical procedure.